In the art of making aluminum complex greases, two methods of preparation were commonly employed. In one of these methods, an aluminum alkoxide is dissolved in an oil stock and two mole equivalents of an acid or acid mixture is added thereto. During subsequent heating, reaction occurred releasing one mole of alcohol per mole of acid introduced. Thereafter to the resulting system water is added which reacts with the final remaining alkoxy group thereby releasing the third and final mole of alcohol and producing a hydroxyl group on the aluminum atom. The alcohol produced is removed by distillation and, since the water is typically added in excess, the excess water is likewise removed by distillation. A typical aluminum alkoxide employed in this method is aluminum isopropoxide; see, for example U.S. Pat. No. 3,345,291 issued to Chevron Research Corporation.
In the second technique, a cyclic aluminum isopropoxide (or other alkoxide) trimer is introduced into a mineral oil. To this mixture is added a carboxylic acid mixture which is approximately equal to two moles of acid per mole of aluminum. When this mixture is heated, reaction occurs which releases one mole of alcohol per mole of aluminum. See, for example, Rinse U.S. Pat. No. 3,054,816. Apparently, it is possible to reverse the order of addition so that the cyclic aluminum isopropoxide trimer is added after the acids are introduced into the petroleum oil; see, for example, column 4 of Bailey et al U.S. Pat. No. 3,776,846. The alcohol thus produced as a by-product is removed by distillation.
Recently, I discovered that certain oxyaluminum acylates can be employed in combination with organic acids to prepare commercially greases of mineral oils in such a way as to avoid the previous problems of removing alcohol produced as a by-product in the grease manufacture and to avoid the addition and/or removal of water present in a system; see my above-identified related U.S. patent application.
Because of such previous problems with alcohol and water, it has not previously been possible to make aluminum complex greases continuously and economically without having to provide special means or techniques for removal of these materials. For example, a continuous process for making lubricating grease has been developed by Texaco, Inc.; see Green et al U.S. Pat. No. 3,475,337 and U.S. Pat. No. 3,475,335 and Witte et al in "The Texaco Continuous Grease Process" presented at the 1979 Annual Meeting of the National Lubricating Grease Institute. This process employs three sections: A reactor section, a dehydration section and a finishing section. As Witte et al state:
"Fatty material, alkali, and a diluent oil are metered into the reactor section where saponification occurs. The stream from the reactor section enters the dehydration section where the water is vaporized, leaving a dehydrated soap base. The dehydrated soap base is then mixed with additional oil and additives in the finishing section and the mixture is thoroughly homogenized, so that a uniform grease is produced."
This process requires extensive mixing in the reactor section which can lead to problems. Apparently, aluminum greases have not been commercially made by this process because of the requirements for sequential addition sections (for acid addition and water addition in the case of the aluminum alkoxide route) and because of the requirement for sequential by-product removal sections (for alcohol and for water) in the aluminum alkoxide route). By eliminating the presence of water and/or alcohol, such as can be accomplished through the use of oxyaluminum acylates in place of, for example aluminum alkoxides, process simplifications and improvements in process sections and conditions become hoped-for possibilities which could not be obtained previously.